568 BACTERIOLOGY. 



bine. They are unstable, becoming gradually inert after 

 withdrawal from the body. 



In consequence of these later investigations the pha- 

 gocytes are again to the fore as one at least of the 

 important defenses of the body and certainly, in so far 

 as the destruction of invading bacteria is concerned, 

 many have come to look upon them as, after all, just 

 what Metschnikoif originally regarded them, the true 

 scavengers of the body. 



Though the destruction of bacteria by the fluids of 

 the body had been demonstrated ; though their inclusion 

 and digestion by phagocytes could readily be observed ; 

 though an antidote for certain of these poisons could 

 be demonstrated in the blood of immunized animals, 

 there was still wanting an explanation of the mechanism 

 through which these interesting phenomena were accom- 

 plished. 



Omitting a group of highly suggestive observations 

 made by many competent investigators, we encounter 

 the most elaborate and at the same time the most fasci- 

 nating effort to interpret the nature of the reactions 

 occurring in the induction of immunity as well as those 

 fundamentally accountable for the natural condition. 



To the genius of Ehrlich * we owe the *' side chain " 

 or "lateral band" (Seitenkettentheorie) theory of im- 

 munity. 



Its fundamental features comprise the acceptance of 

 Weigert's doctrine concerning the mechanism of physio- 

 logical tissue-equilibrium and repair ; and the assump- 

 tion of a specific combining relation, or affinity, between 

 toxic substances and the cells of particular tissues. 



i Ehrlich : Klinisches Jahrbuch, 1897, Bd. vi. Heft 2, S. 809. 



